1. Field of the Invention
This invention relates to a polar group-containing ethylene polymer or copolymer having improved high-voltage insulating characteristics and improved moldability, and to a composition thereof. The invention also relates to a high-voltage cable made by utilization of said ethylene polymer or copolymer or said composition.
More particularly, the present invention relates to a polar group-containing polymer or copolymer having improved insulation resistance and good dielectric breakdown strength, a composition thereof, and a high-voltage power cable made from said polymer or copolymer or said composition.
2. Description of the Prior Art
Heretofore, high-pressure radical polymerization process polyethylene and crosslinked polyethylene are used widely as an insulating material for high-voltage cables because of their excellent electric characteristics.
Nevertheless, the need for continuing improvement in power loss during transmission indicates the need for still further technological progress in high-voltage cables.
One of the means for decreasing such power loss is to increase the insulation resistance of the insulating materials to be used for the production of high-voltage cables.
In recent years, the field of high-voltage cables wherein said cables are used is expanding into such regions where even higher-voltage insulating materials are required. In spite of this fact, the thickness of the insulating layer for high-voltage cables tends to be decreasing year by year because of increasing transportation and installation costs.
Therefore, there is a continuing and growing demand for improving electric properties such as dielectric breakdown strength of a high-voltage insulating layer for power cables to decrease the thickness of the insulating layer.
The present invention is based on a finding that a remarkable improvement of insulation resistance of an ethylene polymer or copolymer can be attained by incorporation of a specific polar group in a specific amount into said ethylene polymer or copolymer.